With reference to the appended FIGS. 1 and 2, the Patent Application FR 2 826 765 describes an image display device including a metallic support plate 1 carrying, on its front face, a plasma discharge display and, on its back face, a discharge power supply and a control means 13 for the display. The plasma display itself includes a front panel 3 and a back panel 4 and has at least a first array of electrodes used notably for maintaining discharges by the application of voltage pulses between adjacent electrodes 7, 8 of two different series of electrodes of this first array, the electrodes having connection ends 11, 12 emerging from one side of said display. The power supply circuit for each pair of adjacent electrodes 7, 8 of two different series forming a current loop starting from the power supply and control means and passing through a first electrode 7 and then a second electrode 8 of the pair,
where the connection ends of the electrodes 7, 8 of the two different series are situated on opposite edges 5, 6 of the display and where, for each pair of adjacent electrodes 7, 8 of two different series, said current loop of the power supply circuit of this pair does not enclose the metallic plate 1.
Preferably, the connection ends of one of the series of electrodes 8 emerging from the side 6 of the display are linked to the power supply and control means 13 by means of transverse electrical conductors 21 placed on the front side of the metallic plate 1 and extending from said ends to the opposite side 5 of the display. All the power supply conductors of the electrodes are brought to the same side of the display and all the electrodes of the array are then able to be connected to the power supply and control means at a same side of the display. A single electrical power supply can thus conveniently be used to generate all the positive and negative (or null) voltage alternations of the sustain pulses.
This device also has the advantage of limiting the eddy current losses in the metallic plate (the current loop does not enclose the metallic plate) while also obtaining discharge regions of identical impedance between adjacent electrodes (current flowing through the same electrode lengths, whichever electrode pair 7, 8 is considered).
In this device, the transverse conductors are generally grouped into one or more banks of conductors. In FIG. 2, two banks of conductors 23, 24 of reduced width are provided, for example, and are disposed parallel to the base of the plasma display between the sides 5 and 6 to link the display power supply and control means 13 to the connection ends 12 of the series of electrodes 8, which are common electrodes, on the side 6 of the display. One of these banks of conductors is disposed in the upper part of the display and the other in the lower part. Furthermore, they are both inserted between the display back panel 4 and the metallic plate 1. It should be noted that, in this figure, the display power supply and control means 13 are shown beside the plasma display in order to show their connections to the banks of conductors 23 and 24, whereas they are, of course, in reality situated behind the metallic plate 1, as indicated in FIG. 1.
Given the position of the banks of conductors 23 and 24 with respect to the plasma display, differences in luminance between the display area situated at the same level as a bank of conductors and the display area situated between the banks of conductors may be observed. This is caused by differences in inductance between the current loops of the power supply circuits of the various pairs of adjacent electrodes 7, 8. Indeed, the power supply circuit of each pair of adjacent electrodes 7, 8 forms a current loop starting from the power supply and control means 13 passing through a first electrode 7 followed by the second electrode 8 of the pair, then through one of the banks of conductors 23, 24, before closing itself back at the power supply and control means 13. For the pairs of electrodes 7, 8 located near to the banks of conductors, the corresponding current loops have a smaller surface area and hence a lower inductance. The current loops associated with the pairs of electrodes 7, 8 that are located further away from the banks of conductors have a greater surface area. These current loops therefore exhibit a higher inductance. Given that the shape of the discharge in the plasma display discharge regions is very sensitive to this variation in inductance, this leads to a disparity in the light emission and hence a difference in the luminance between the plasma display discharge regions that are near to the banks of conductors and the other plasma display discharge regions.
One solution could be to provide a bank of conductors covering the entire surface of the display so as to only create current loops of minimal surface area. However, this solution has numerous drawbacks, notably a high material and production cost and a high parasitic capacitance is created between the common electrodes 8 and the bank on the one hand, and the metallic plate 1 on the other.